[codex] Record external agent import results (#28396)

## Summary
- restore `externalAgentConfig/import/progress` notifications while
keeping `externalAgentConfig/import/completed` as the must-deliver event
- persist completed external-agent config imports in state DB by
`importId`, including concrete success/failure details for config,
AGENTS.md, skills, plugins, MCP servers, subagents, hooks, commands, and
sessions
- add `externalAgentConfig/import/readHistories` so clients can recover
persisted import results after missing the live completion notification
- include `errorType` on import failures in protocol
responses/notifications and persisted DB JSON so future code can
classify failures without another wire/storage shape change

## Validation
- `git diff --check`
- `just test -p codex-state external_agent_config_imports`
- `just test -p codex-app-server-protocol`
- `CODEX_SQLITE_HOME=/private/tmp/codex-app-server-sqlite-read-details
just test -p codex-app-server
external_agent_config_import_sends_completion_notification_for_sync_only_import`

Also ran earlier broader checks before publishing:
- `just test -p codex-state`
-
`CODEX_SQLITE_HOME=/private/tmp/codex-app-server-external-agent-test-sqlite
just test -p codex-app-server external_agent_config`
- `just test -p codex-external-agent-migration`

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json

@@ -2124,6 +2124,29 @@
           "title": "ExternalAgentConfig/importRequest",
           "type": "object"
         },
+        {
+          "properties": {
+            "id": {
+              "$ref": "#/definitions/v2/RequestId"
+            },
+            "method": {
+              "enum": [
+                "externalAgentConfig/import/readHistories"
+              ],
+              "title": "ExternalAgentConfig/import/readHistoriesRequestMethod",
+              "type": "string"
+            },
+            "params": {
+              "type": "null"
+            }
+          },
+          "required": [
+            "id",
+            "method"
+          ],
+          "title": "ExternalAgentConfig/import/readHistoriesRequest",
+          "type": "object"
+        },
         {
           "properties": {
             "id": {
@@ -4834,6 +4857,26 @@
           "title": "RemoteControl/status/changedNotification",
           "type": "object"
         },
+        {
+          "properties": {
+            "method": {
+              "enum": [
+                "externalAgentConfig/import/progress"
+              ],
+              "title": "ExternalAgentConfig/import/progressNotificationMethod",
+              "type": "string"
+            },
+            "params": {
+              "$ref": "#/definitions/v2/ExternalAgentConfigImportProgressNotification"
+            }
+          },
+          "required": [
+            "method",
+            "params"
+          ],
+          "title": "ExternalAgentConfig/import/progressNotification",
+          "type": "object"
+        },
         {
           "properties": {
             "method": {
@@ -9089,6 +9132,52 @@
         "title": "ExternalAgentConfigImportCompletedNotification",
         "type": "object"
       },
+      "ExternalAgentConfigImportHistoriesReadResponse": {
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "properties": {
+          "data": {
+            "items": {
+              "$ref": "#/definitions/v2/ExternalAgentConfigImportHistory"
+            },
+            "type": "array"
+          }
+        },
+        "required": [
+          "data"
+        ],
+        "title": "ExternalAgentConfigImportHistoriesReadResponse",
+        "type": "object"
+      },
+      "ExternalAgentConfigImportHistory": {
+        "properties": {
+          "completedAtMs": {
+            "format": "int64",
+            "type": "integer"
+          },
+          "failures": {
+            "items": {
+              "$ref": "#/definitions/v2/ExternalAgentConfigImportItemTypeFailure"
+            },
+            "type": "array"
+          },
+          "importId": {
+            "type": "string"
+          },
+          "successes": {
+            "items": {
+              "$ref": "#/definitions/v2/ExternalAgentConfigImportItemTypeSuccess"
+            },
+            "type": "array"
+          }
+        },
+        "required": [
+          "completedAtMs",
+          "failures",
+          "importId",
+          "successes"
+        ],
+        "type": "object"
+      },
       "ExternalAgentConfigImportItemTypeFailure": {
         "properties": {
           "cwd": {
@@ -9097,6 +9186,12 @@
               "null"
             ]
           },
+          "errorType": {
+            "type": [
+              "string",
+              "null"
+            ]
+          },
           "failureStage": {
             "type": "string"
           },
@@ -9165,6 +9260,26 @@
         "title": "ExternalAgentConfigImportParams",
         "type": "object"
       },
+      "ExternalAgentConfigImportProgressNotification": {
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "properties": {
+          "importId": {
+            "type": "string"
+          },
+          "itemTypeResults": {
+            "items": {
+              "$ref": "#/definitions/v2/ExternalAgentConfigImportTypeResult"
+            },
+            "type": "array"
+          }
+        },
+        "required": [
+          "importId",
+          "itemTypeResults"
+        ],
+        "title": "ExternalAgentConfigImportProgressNotification",
+        "type": "object"
+      },
       "ExternalAgentConfigImportResponse": {
         "$schema": "http://json-schema.org/draft-07/schema#",
         "properties": {